{{thtitle|Touhou |Suimusou|ruby=Gathering Reverie<ref>Double meaning in the title: "萃夢" (''suimu'', "gathering dream") is a homophone of "酔夢" (''suimu'', "drunken dream")</ref>| ~ Immaterial and Missing Power|jp=東方萃夢想 ～ Immaterial and Missing Power}} is the 7.5th installment of the ''[[Touhou Project]]'' by [[Team Shanghai Alice]]'s sole member [[ZUN]] along with conjunction with [[Twilight Frontier]]. It is called "7.5" because the events chronologically take place between ''[[Perfect Cherry Blossom]]'' (TH07) and ''[[Imperishable Night]]'' (TH08). It was developed alongside ''Imperishable Night'', and released at the following Comiket 67.

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{{thtitle|Touhou |Suimusou|ruby=Gathering Reverie<ref>Double meaning in the title: "萃夢" (''suimu'', "gathering dream") is a homophone of "酔夢" (''suimu'', "drunken dream")</ref>| ~ Immaterial and Missing Power|jp=東方萃夢想 ～ Immaterial and Missing Power}} is the 7.5th installment of the ''[[Touhou Project]]'' by [[Team Shanghai Alice]]'s sole member [[ZUN]] along with conjunction with [[Twilight Frontier]]. It is called "7.5" because the events chronologically take place between ''[[Perfect Cherry Blossom]]'' (TH07) and ''[[Imperishable Night]]'' (TH08). It was developed alongside ''Imperishable Night'' and released at the following Comiket 67.

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Immaterial and Missing Power differs from the other games in the Touhou Project. Instead of being one of the series' traditional shoot 'em up games, it is a 2D fighting game with a heavy bias toward projectiles. Because of this slant, the spell card feature from the series' other installments also plays a role in this one. In addition to being a player's means of using special attacks, after getting opponents down to a certain amount of HP in Story Mode, they will unleash a spell card, which involves trickier attack patterns and must be overcome to defeat them for good. As the story goes on, enemies will have multiple spell cards.

Immaterial and Missing Power is the first Touhou Project game to be numbered with a decimal. Though it was released after Imperishable Night, the events of the game chronologically occur between it and Perfect Cherry Blossom, during the summer of that year.

The game was a collaboration between ZUN's Team Shanghai Alice and Twilight Frontier. ZUN worked on the scenario, Suika Ibuki's character design, the spell cards, and a few pieces of music. He also supervised the rest of the elements of the game, though granting the members of Twilight Frontier an amount of freedom in the process. In addition, he worked on various graphics and some of the programming.[2]

Gensokyo has settled down after the Spring Snow Incident that occurred in Perfect Cherry Blossom. Reimu Hakurei and the others are currently having a feast every three days at the Hakurei shrine. During these feasts, a strange mist appears. The playable character decides to get the cause of the never-ending feast schedule and the mist. This incident was later called the "Night Parade of One Hundred Oni Every Four Days" by Aya Shameimaru in Bohemian Archive in Japanese Red.

The perpetrator of the incident is an oni, said to have disappeared from Gensokyo, named Suika Ibuki. She thought that it was a shame that the flower-viewing season had been cut short due to the very long winter. She spread herself out in the form of a mist all throughout Gensokyo, and "gathered" the hearts of both humans and youkai to cause them to have a feast every few days.

Because the art of oni extermination has been lost to Gensokyo, the girls could not eliminate her, but the mist disappeared afterwards and feasts started to happen less frequently.

The music of Immaterial and Missing Power has a total of 34 tracks included. Generally, there's a theme for the night time of each stage, along with a different theme for the day time of the same stage, which are associated to the character.

It consists generally of arrangements of previous Touhou songs by two composers from Twilight Frontier named NKZ and U2, along with including original soundtracks created by themselves. ZUN composed the boss themes Demystify Feast, Night Falls ~ Evening Star (Yukari Yakumo's theme), and Oni's Island in the Fairyland ~ Missing Power (Suika Ibuki's theme). He comments that his songs felt somewhat out of place among the other arrangements.[2]

A very early trial of the game was released on April 18, 2004 at the first Reitaisai alongside the initial trial of Imperishable Night. Later on at that summer's Comiket, a more full-featured trial was released. Finally, at Comiket 67 on December 30, 2004, the full version saw its release at both the event and in doujin stores. Many patches were released afterwards, culminating in the final v1.11 patch that included Hong Meiling as a playable character, though without a story mode.